1. Field of the Invention
This invention relates to a process of forming a plasma polymerized film on a substrate surface by using a plasma of an organic compound gas, or a process of forming a film on a substrate surface by using an inorganic compound gas, as exemplified by plasma CVD. More particularly. it is concerned with a film formation process that can form the above every sort of film on a substrate in a high energy efficiency and is particularly suited for forming a film comprising a diamond-like substance.
2. Description of the Prior Art
Hitherto utilized in forming films by using every sort of plasma are methods in which parallel plate electrodes, hollow cathode cylindrical electrodes (which are for use in direct current, low frequency or high-frequency electric sources), coils (for use in high-frequency electric sources), microwave cavities (for use in microwave electric sources) or the like are used to generate plasma.
Such conventional methods of forming films by using plasma, however, can not treat substrate surfaces having a relatively large area. and moreover these methods have the problem that they can achieve only a low energy efficiency.
More specifically, when, for example, the microwave cavities are used, the plasma that can be generated has inherently such a small volume that they are not suited for treating surfaces having a large area. Other plasma generating systems enable generation of plasma with a large volume. Since, however, only part of the plasma that comes into contact with the substrate, can substantially contribute to the formation of films on substrate surfaces, it often occurs that almost all part of the large volume plasma plays no part in the formation of films, resulting in a low energy efficiency. In particular, in instances in which the formation of films is carried out in a high-temperature plasma zone, the plasma has such a high energy density that making plasma having a large volume may bring about a remarkable increase in consumption of the electric power necessary for excitation. Thus, this is a great problem in practical viewpoints.
In particular, films comprising a diamond-like substance are expected to be put into practical use as diamond tools such as throw-away tips and saws, all sorts of sliding parts, heat dissipation plates used in devices such as semiconductor lasers, IC packages and hybrid ICs, etc. For that purpose, however, it is strongly required to make it possible to prepare a diamond-like substance having a large area, and to improve productivity and enhance economical merits. However, in the above conventional method utilizing microwave plasma, the plasma that can be generated has inherently a small volume since there is used a microwave cavity. Hence, a film obtainable by making treatment once can have only a film area as small as several square centimeters, and can be applied with difficulty when substrates have a large substrate surface as in large tools, large machine parts, etc. Also, even when the substrates to be treated are of small size, it is impossible to treat a large number of substrates in one time, bringing about the problem that there can be achieved low productivity and economical merits. Moreover, an attempt to make large the microwave cavity may result in a lowering of energy absorption efficiency, making it impossible to generate a high temperature plasma necessary for the formation of films.